Updating Trackable::association_hash to write through parent.

lib/mongoid/history/trackable.rb

@@ -133,18 +133,18 @@ def traverse_association_chain(node=self)
       end
 
       def association_hash(node=self)
-        # get all reflections of embedded_in association metadata
-        # and find the first association that matches _parent.
-        if node._parent
-          meta = node.reflect_on_all_associations(:embedded_in).find do |meta|
-            node._parent == node.send(meta.key)
-          end
 
-          inverse = node._parent.reflect_on_association(meta.inverse) if meta
+        # We prefer to look up associations through the parent record because
+        # we're assured, through the object creation, it'll exist. Whereas we're not guarenteed
+        # the child to parent (embedded_in, belongs_to) relation will be defined
+        if node._parent
+          meta = _parent.relations.values.select do |relation|
+            relation.class_name == node.class.to_s
+          end.first
         end
 
         # if root node has no meta, and should use class name instead
-        name = meta ? meta.inverse.to_s : node.class.name
+        name = meta ? meta.key.to_s : node.class.name
 
         { 'name' => name, 'id' => node.id}
       end

spec/integration/integration_spec.rb

@@ -382,6 +382,16 @@ class Tag
         @post.tags.count.should == 1
         @post.history_tracks.last.action.should == "destroy"
       end
+
+      it "should write relationship name for association_chain hiearchy instead of class name when using _destroy macro" do
+        update_hash = {"tags_attributes" => { "1234" => { "id" => @tag_foo.id, "_destroy" => "1"} } }
+        @post.update_attributes(update_hash)
+
+        # historically this would have evaluated to 'Tags' and an error would be thrown
+        # on any call that walked up the association_chain, e.g. 'trackable'
+        @tag_foo.history_tracks.last.association_chain.last["name"].should == "tags"
+        lambda{ @tag_foo.history_tracks.last.trackable }.should_not raise_error
+      end
     end
 
     describe "non-embedded" do